Well, it depends on the shot. If you get a net cord when you hit a smash, then it's just luck. I don't believe any player in the world is capable of doing that deliberately (not without throwing away a lot of points for nothing, anyway...). If you get a net cord from a shot played very near the net, however, then sometimes it's not just luck. When I'm able to hit the shuttle at net height, only a few inches away from the net, with myself in a balanced position, then I aim for the very top of the cord or just above. I get a lot of net cords that way, but rarely make an error. That's what the commentators mean when they say, "he made his own luck": the player got there early, on balance, and was able to play his shot from very near the net. In that situation, he has a decent chance of getting a net cord (perhaps 20%, in a good position. Sometimes it can be more).